Xamarin FAQ, 2015-11 - “Xamarin Starter is our free tier that allows developers to build and publish simple apps that contain no more than 128k of compiled user code (IL), don't call out to native third party libraries (i.e., developers may not P/Invoke into C/C++/Objective-C/Java), and are built using Xamarin.iOS / Xamarin.Android (not Xamarin.Forms). Xamarin Starter installs automatically with Visual Studio 2015, and works with VS 2012, 2013, and 2015 (including Community Editions)”.

StackOverflow "Is Xamarin free in Visual Studio 2015?" - “Actually, we expanded our Starter edition to work now in Visual Studio for building smaller iOS and Android apps for free. This does not include Xamarin.Forms though, which is only available in the trial or any paid subscription”.

Answer: “It's per application. When you build an iOS or Android executable project, the build process scans the executable and finds the assemblies it uses in order to includes them in the app. The executable and the assemblies it references are all are all counted towards the size limit, with the exception of the assemblies that are part of the framework. Note that even if the linker is set to removed unused methods from user code, the size calculation is performed before this takes place”.

Comment: “You wouldn't be able to use even MonoGame for example in the starter edition”.

Experts told me that the tool originally was intended for learning XAML. Thats why it is no GUI designer, but you must know the XAML syntax precicely, without any tool support, to create a GUI interface...

ComponentSource - Forums - “You are not currently subcribed to any Discussion Forums. ComponentSource Forums are available on each product within the Product Catalog” → Top menu bar item “Support Forum”.